1. Field of the Invention
This invention relates to telecommunication systems in which voice and telephony traffic are carried over a data network. More particularly, the invention concerns an improvement in VTOA (Voice and Telephony Over ATM) gateways.
2. Description of the Prior Art
The infrastructure and technology of the current Public Switched Telephone Network (PSTN) is evolving from a wholly circuit switched model to a model that includes packet-based networking, particularly for trunking between End Office (EO) switches. The use of flexible and cost-effective packet-based networks allows for the convergence of voice and data while maintaining the convenience, reliability and quality-of-service of circuit-switching. ATM (Asynchronous Transfer Mode) networks are currently the preferred choice for building packet-telephony systems because of their high bandwidth, efficiency and Qos (Quality of service).
A VTOA Packet Voice Gateway (PVG) is a gateway system that interconnects circuit switched network components, such as End Offices, to an ATM core network. The PVG has a TDM interface connected to the circuit switched network, an ATM interface connected to the ATM network, and an interworking system for converting between the TDM and ATM protocol formats. The interworking system typically comprises one or more processor controlled circuit boards that manage the conversion between AAL (ATM Adaptation Layer) 1/2 bearer traffic (voice) and AAL 3/4/5 data traffic on the ATM network side, and TDM bearer/data traffic on the circuit-switched network side. Signaling is typically handled by a Control Gateway (CG) that interworks between the narrowband signaling of the circuit-switched network (e.g., ISDN, QSIG, A/B) and the AAL5 UNI broadband signaling used in the ATM network. The CG may either reside on a separate host from the PVG, or on the same host, in which case the PVG circuit board(s) will typically connect to the CG circuit board via a common backplane bus, (e.g., VMEbus, CompactPCI, FutureBus, to name a few). The PVG (also known as a media gateway) and the CG communicate with each other using a standard media gateway control protocol such as Megaco (Media gateway control protocol or H.248) and IPDC (IP Device Control).
Separate processing of different AAL layers by independent circuit boards controlled by localized software is not particularly efficient, even when the PVG and CG circuit boards are resident on the same hardware platform. It would be desirable to simplify such processing using an integrated approach, preferably allowing all AAL layers to be processed through a single circuit board controlled by single set of integrated software routines.